Ava Gadro is performing a titration in order to determine the amount of sodium hydroxide, NaOH(aq), in 81 mL of an aqueous solution. If Ava used 27 mL of a 0.15 M HCl(aq) solution as her titrant to reach the equivalence point, what was the concentration of sodium hydroxide in the initial solution?

M = 0.050 M

Explanation:

WE have an acid base reaction between NaOH and HCl. The reaction is as follow:

HCl + NaOH > NaCl + H₂O

As we can see, we have a balanced equation already, and we can also see that the mole ratio between the HCl and NaOH is 1:1, therefore we can use the following expression:

M₁V₁ = M₂V₂       1: acid;   2: base

This expression is used when the reactions has reached the equivalence point. As we want to know the concentration of the base, we just solve for M₂ above so:

M₂ = M₁V₁ / V₂

All we have to do now is replace the given values and solve for the concentration:

M₂ = 0.15 * 27 / 81